1. Field of the Invention
This invention relates to a device for testing the performance accuracy of components in an automotive collision avoidance radar system.
2. Description of the Related Art
A collision avoidance radar operates by transmitting a signal from an antenna typically located in the grill area of an automobile. The collision avoidance radar then determines from a return signal received a distance an object is located from an automobile and a rate the object causing the return signal is moving relative to the automobile.
Collision avoidance radars in the United States are configured to operate within a narrow band millimeter frequency range of 76-77 GHz allocated by the Federal Communications Commission (FCC). To assure proper performance of a collision avoidance radar system, testing is periodically performed to assure components of the system are operating within the 76-77 GHz range specified by the FCC. Testing is further periodically performed to assure that the system is radiating adequate power and to pinpoint components which are not functioning properly if the system is not providing adequate power, or operating outside desired frequency ranges. Such testing is typically performed using a vector network analyzer (VNA).
Components typically used in a VNA setup to make measurements in the 76-77 GHz range are shown in FIG. 1. The typical VNA illustrated includes an external millimeter wave reflectometer 110 whose stimulus is provided from a signal synthesizer 100 located external to the reflectometer 110. The local oscillator (LO) input to the reflectometer 110 is provided from a tunable synthesizer 112, also located separate from the reflectometer 110. VNAs that include components to make measurements in the millimeter range, as shown in FIG. 1, include the ANRITSU(trademark) 37000 and ANRITSU(trademark) 360 series VNAs manufactured by Anritsu Company of Morgan Hill Calif. Other VNAs having components shown in FIG. 1 include the HP 8510m series VNAs manufactured by Hewlett Packard.
The reflectometer 110 includes millimeter wave multipliers 102 and 104 providing the signal from the synthesizer 100 to a device under test (DUT) 104. The multipliers 102 and 104 multiply the frequency of a signal from the synthesizer by a factor of four or more to achieve a 76-77 GHz output. The DUT 104 is connected to the reflectometer 110 using WR-12 wave guide forming test ports 106 and 107 to provide the 76-77 GHz output. The synthesizer 100 is connected to the reflectometer 110 using coaxial connectors. Amplifiers, isolators, attenuators, and couplers are further provided in the path between the coaxial connector inputs and WR-12 waveguide test ports 106 and 107, as shown in FIG. 1.
Intermediate Frequency (IF) output signals are provided from the reflectometer 110 using superheterodyne harmonic millimeter wave mixers 121-124. The LO signal from synthesizer 112 is provided to one input of each of the mixers 121-124 through amplifiers, isolators, and power dividers as shown in FIG. 1. The IF signals from the mixers 121-124 are provided back to a VNA for further down-conversion and processing.
The couplers 131-134 provide a second input to each one of the mixers 121-124. Couplers 131 and 133 couple an incident signal traveling from multipliers 102 and 104 to mixers 121 and 123. Couplers 132 and 134 couple signals reflected from the DUT 104 or transmitted through the DUT 104 to the mixers 122 and 124.
The performance of the system shown in FIG. 1 is limited in several ways. First, the frequency switching time for the synthesizer 100 is typically slow (xcx9c5 to 15 milliseconds). The slow switching speed is due to high resolution available over a broad bandwidth of signals typically provided from the instrument grade synthesizer 100. Second, the nonlinearity of multipliers 102 and 104 prevent the signal provided to the test ports 106 and 107 from having a flat output power as a function of frequency. Third, a harmonic higher than the first order is typically required from harmonic mixers 121-124 so that a lower frequency LO signal from the LO synthesizer 112 can achieve a desired IF output frequency. Using a higher order harmonic from the mixers 121-124 results in a significant conversion loss. Fourth, the cost of instrument grade synthesizers typically used for the stimulus synthesizer 100 and local oscillator synthesizer 112 in a VNA can be excessive.
The present invention provides a test system used with a stimulus synthesizer operating over a narrow frequency range. With a narrow bandwidth stimulus synthesizer, frequency switching time can be increased. Further, the cost of the stimulus synthesizer can be reduced relative to a broadband instrument grade synthesizer. Further, a synthesizer referenced to the stimulus synthesizer can be used to provide the LO with a significant cost reduction over an instrument grade LO synthesizer.
The present invention further provides a test signal from the stimulus synthesizer to a DUT without an intervening multiplier, enabling a flat power output as a function of frequency.
The present invention further uses a fundamental or a first harmonic for all up-conversions and down-conversions so conversion losses can be avoided.
The present invention is a test system including a narrowband SCORPION(trademark) VNA manufactured by Anritsu Company, a dielectric resonator oscillator (DRO) for providing a LO signal, and a test module.
The Scorpion VNA includes a stimulus synthesizer producing a test signal ranging from 3 GHz to 6 GHz to selectively provide at two input ports of the test module. The Scorpion VNA further receives 3 to 6 GHz IF output signals from the test module and down-converts these signals to provide to a DSP.
The test module includes linear up-converters to translate the 3 to 6 GHz output signal from the Scorpion VNA to provide signals in a 75-78 GHz range to test ports of the test module. The test module avoids multipliers between the VNA and test ports of the test module to create a flat output power vs. frequency signal.
The DRO for providing the LO signal produces a 18 GHz output phase locked to the Scorpion VNA crystal oscillator. The 18 GHz is multiplied times four to 72 GHz. The 72 GHz Lo is used to up-convert the 3 to 6 GHz output of the Scorpion system to a 75 to 78 GHz frequency band. Down-converters further use the 72 GHz LO to translate the 75 to 78 GHz signal from the test module to IF signals in the 3 to 6 GHz range to be detected and measured by the Scorpion VNA.